Pedestal mounted rocker arm assemblies have a rocker aim rotatably mounted on a support pin which in turn is fixed to a cylinder head through a pedestal. The support pin is also known as a trunnion. Conventionally, the support pin rests on the pedestal, also known as a support block, which positions the overall rocker arm assembly away from the cylinder head. One end of the rocker arm is in contact with the push rod while the other end of the rocker arm is in contact with a valve shaft.
Roller bodies, also referred to as radial bearings, are conventionally used between the support pin and the rocker arm to facilitate rotational movement of the rocker arm on the support pin and to handle radial loads.
Moreover, an inner sleeve and an outer sleeve can be used. When incorporated into the rocker arm assembly, the inner sleeve and the outer sleeve are positioned between a through-hole in the rocker arm with the inner sleeve affixed to the support pin and the outer sleeve affixed to the rocker arm. Furthermore, the roller bodies are positioned between the inner sleeve and outer sleeve to accommodate radial loads.
Rocker arm assemblies can also be subject to axial forces or thrust forces. Axial forces occur when certain parts are out of alignment, for example, when the rocker arm pallet and the socket, the lower end of the push rod and the socket, or the valve shaft and the rocker arm pallet are out of alignment. Such rocker arm assemblies are often referred to as “offset rocker arm assemblies.” Thrust forces occur at thrust surfaces. The thrust surfaces are present on the ends of the support pin and on the inner sleeve and outer sleeve adjacent to the ends of the support pin.
During a valve event, the push rod of the engine engages the rocker arm at an angle relative to the support pin centerline such that thrust and moment loads are generated with respect to the bearing axis, attempting to translate the rocker arm along the bearing axis. The loads resulting from the valve event vary as a function of engine speed, valve spring compression, and pushrod articulation during the valve event. The outer sleeve is fixed to the rocker arm and, therefore, translates with the rocker arm until contact is made with the inner sleeve, which is fixed to the support pin. The outboard flange on the inner sleeve experiences compressive loading imparted by the outer shell. The rolling elements carry radial forces generated by the combination of the pushrod and the valve spring during the valve event while permitting low friction articulation of the rocker arm for valve actuation.
To ensure the support pin, which typically has a flat upper surface and a concave lower surface that contacts the pedestal, does not become inverted prior to final installation a captured fastener is commonly affixed in a centrally located bore in the support pin. Essentially, a captured fastener is a washer that has a circular flange extending from one side of the washer with threading on the inside of the flange. A bolt is also typically inserted in the captured fastener and the bore prior to final assembly.
Furthermore, snap rings, wave springs, or diaphragm (Belleville) springs can be used to control the axial loads of a shaft assembly. Shaft assembly arms typically utilize journal bearing pivots, though needle bearing applications are also known. However, shaft assemblies usually require oil galleries for arm bearing lubrication which adds to the overall cost of the use of the snap ring or spring application.
Rocker arm assemblies utilizing a captured fastener are known, see, for example, U.S. Pat. No. 6,694,936 and U.S. Patent Application No. 2008/0098971. Such rocker arms employ a captured fastener and a fastening bolt to ensure the support pin does not become inverted prior to final installation of the rocker arm to the engine. The manufacturability of captured fasteners is challenging due to the precise flange geometry required for fastening with the bore of the support pin. Also, the use of the captured fastener and fastening bolt adds to the cost and packaging size of the rocker arm assembly. Furthermore, in certain instances, captured fasteners cannot be used.
Additionally, see, for example, U.S. Pat. No. 5,437,209, which discloses a rocker arm assembly. The support pin of the rocker arm assembly has a D-shaped feature at each end to prevent the support pin from inverting. The support pin engages in a D-shaped hole stamped into the outer bearing sleeve, coupled with an inner bearing sleeve that has a specified range of diametric clearances to the support pin journal, preventing the support pin from inverting. However, the design only applies to an inner sleeve that has a clearance to the support pin, the manufacturability is costly due to intricacies of the design, and the time consuming assembly.